Nephrology - Kidney Stones Category: Health Condition/ Disease - Kidney Stones Practice Questions Key Practice Point #1 ...
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Nephrology - Kidney Stones
Category: Health Condition/ Disease
Practice Questions
Q1: What dietary factors have been associated with a decreased risk of developing renal calculi
(kidney stones) in individuals with no previous history of kidney stones?
Subcategory: Intervention
Updated: 2014-07-03
Key Practice Point #1
Observational data suggests that a high fluid intake (>2500 mL/day) decreases the risk for kidney stones
in adults with no previous history of kidney stones.
When examining associations between the type of beverage consumed, observational data suggests a
decreased risk of kidney stones with a high consumption of fluids such as orange juice, coffee,
decaffeinated coffee, tea, wine (red and white) and beer compared to low consumption of these fluids. No
clinical trials have been conducted to assess the effectiveness of increased water intake for the primary
prevention of kidney stones. No recommendations can be made regarding the amounts of specific
beverages to consume to reduce the risk of kidney stones.
See Additional Content:
What role does alcohol play in the prevention of kidney stones in individuals with no history of kidney
stones and for individuals with a history of developing kidney stones?
What role does caffeine play in the prevention of kidney stones in healthy individuals with no history of
kidney stones and for individuals with a history of developing kidney stones?
Grade of Evidence: C
Evidence
a. Observational data from the Health Professionals Follow-up Study (HPFS) of 40- to 75-year-old
men with no previous history of kidney stones (n=45,619), demonstrated that fluid intake was
inversely associated with the risk of kidney stones (RR for men in the highest compared to the
lowest quintile for fluid intake (average 2538 mL/day and 1275 mL/day, respectively) =0.71; 95%
CI, 0.52 to 0.97) (1). Follow-up data confirmed this trend (2).
b. The Nurses’ Health Study I (NHS I) of women aged 34 to 59 years (n=91,731) with no history of
kidney stones found that fluid intake was inversely associated with the risk for kidney stones (RR
for stone formation in women in the highest quintile of fluid intake compared with women in the
lowest quintile (average 2592 mL/day and 1412 mL day respectively) =0.61; 95% CI, 0.48 to
0.78) (3). A similar association was observed in younger women (aged 27 to 44 years) in the
NHS II (n=96,245) (4).
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 1c. Analysis of data obtained from the HPFS and NHS I and II (n=194,095) over a median follow up of
eight years examined the association between the type of beverage consumed and the risk of
kidney stones (5). Comparing the highest (i.e. ≥1 serving /day) to lowest consumption (i.e.7. Borghi L, Meschi T, Maggiore U, Prati B.Dietary therapy in idiopathic nephrolithiasis. Nutr Rev.
2006 Jul [cited 2013 Jul 2];64(7 Pt 1):301-12. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/16910218
Key Practice Point #2
Observational data suggests that a high intake of dietary calcium (>1000 mg/day) from dairy and non-dairy
sources decreases the risk for kidney stones in individuals with no previous history of stones.
In contrast, observational studies and one clinical trial conducted in postmenopausal women suggests
that the intake of supplemental calcium (≥1000 mg/day) may increase the risk of kidney stones,
particularly when the supplement is taken on an empty stomach as this action promotes oxalate binding.
Current recommendations are to achieve the Dietary Reference Value for calcium [See Comments].
See Additional Information: What dietary and lifestyle factors have been associated with an increased risk
of developing renal calculi (kidney stones) in individuals with no previous history of kidney stones?
Grade of Evidence: C
Evidence
a. Observational data from the Health Professionals Follow-up Study (HPFS) of 40- to 75-year-old
men with no previous history of kidney stones (n=45,619), demonstrated that dietary calcium
intake was inversely associated with the risk of kidney stones (RR for men in the highest as
compared with the lowest quintile group for calcium intake (average 1326 mg/day and 516
mg/day, respectively) =0.56; 95% CI, 0.43 to 0.73) (1). This reduced risk remained after
adjustment for alcohol consumption, and dietary intake of animal protein, potassium and fluid.
Fourteen year follow-up data in the same cohort demonstrated a reduced risk of kidney stones
associated with calcium intake only for mento the timing of calcium ingestion relative to the amount of oxalate consumed. However, other
factors present in dairy products could also be responsible for the decreased risk observed with
dietary calcium. In an examination of younger women aged 27 to 44 years with no history of
kidney stones from the NHS II (n=96,245), after adjusting for other relevant risk factors a higher
intake of dietary calcium was also associated with a reduced risk of kidney stones (RR for
women in the highest quintile of intake of dietary calcium compared with women in the lowest
quintile = 0.73; 95% CI, 0.59 to 0.90) (4). In this cohort, supplemental calcium intake was not
associated with risk of stone formation.
c. More recent analysis (published in 2013) of the HPFS (excluding men ≥60 years), NHS I and II
examined associations of dietary calcium from non-dairy and dairy sources and risk of kidney
stones over a combined follow up of 56 years (5). Comparing the highest to lowest quintile
intake of non-dairy dietary calcium (i.e. average intake ~430 mg/day versus 250 mg/day) was
associated with a reduced risk of kidney stones in all cohorts (HPFS: RR, 0.71; NHS I: RR,
0.82, and NHS II: RR, 0.74). Similar associations were observed when comparing the highest to
lowest quintile of dairy calcium (i.e. average intake of ~850 mg/day versus 280 mg/day) in all
cohorts. The authors conclude that higher dietary calcium from either non-dairy or dairy sources
were independently associated with a reduced risk of kidney stones.
d. The Women's Health Initiative (WHI) was an RCT of 18,176 postmenopausal women who
received calcium (1000 mg/day) and vitamin D (400 IU/day) or placebo for an average of seven
years (6). Women recruited into the study were healthy at baseline with no history of urinary
tract stones; however, later review found that 161 participants in the supplementation group and
172 in the control group had a self-reported history of urinary tract stones (these individuals were
included in the analysis which was conducted on an intention-to-treat basis). Results showed
that women in the supplementation group had a 17% increased risk of developing urinary tract
stones (95% CI, 2% to 34%) than the placebo group. No differences in incidence of stones was
observed when other factors were considered, including demographic (e.g. age, ethnicity,
education, smoking status) medical history, BMI, dietary intake (e.g. total energy, protein, fat,
alcohol, caffeine, vitamin C, calcium, sodium, iron, potassium, oxalic acid) or use of calcium
supplements at baseline.
Comments
The 2010 Institute of Medicine report on calcium and vitamin D found evidence to support a possible
increased risk of kidney stones with high doses of calcium, when dietary intake of calcium plus
supplements is greater than 2000 mg/day (7). This evidence was from the study of postmenopausal
women (aged 50-70 years), who were consuming calcium from foods and adding calcium supplements to
this baseline amount (6), and should be interpreted with the recognition that dietary calcium does not
increase the risk of kidney stones. As a result, the UL for calcium for adults over the age of 50 was set at
2000 mg/day (7).
Although kidney stones occur more often in younger adults (aged 19-50 years) than in older adults, the
formation of kidney stones in younger adults (aged 19-50 years) does not appear to be linked to calcium
supplement use. Therefore, the UL for this group was set at 2500 mg/day, midway between the UL for
adolescents (3000 mg/day) and that of older adults (7).
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 4In general, the committee warns that total calcium intakes over 2000 mg/day may increase the risk for
kidney stones, while not conferring any additional benefit for bone health.
Rationale
With a high calcium intake, calcium binds oxalate in the gastrointestinal tract and the calcium-oxalate
complex is excreted in the feces. Consequently, intestinal oxalate absorption is reduced with a
subsequent reduction in urinary oxalate excretion (3). In contrast, low dietary calcium intake results in
hyperabsorption of free oxalate, leading to the formation of insoluble nonabsorbable calcium oxalate
complexes and increased urinary oxalate excretion (8).
The difference in findings between dietary and supplemental calcium have been attributed to different
timing of ingestion, whereby ingesting supplements without food leads to increased calcium absorption
and urinary excretion with no effect on absorption and excretion of oxalate (8). It is also possible the dairy
products also contain other inhibitory factors.
References
1. Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and
other nutrients and the risk of symptomatic kidney stones. N Engl J Med. 1993 Mar 25 [cited
2013 Jul 2];328(12):833-8. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/8441427
2. Taylor E, Stampfer M, Curhan G. Dietary factors and the risk of incident kidney stones in men:
new insights after 14 years of follow up. J Am Soc Nephrology. 2004 Dec [cited 2013 Jul
2];15:3225-32. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15579526
3. Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary
calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney
stones in women. Ann Intern Med. 1997 Apr 1 [cited 2013 Jul 2];126(7):497-504. Abstract
available from: https://www.ncbi.nlm.nih.gov/pubmed/9092314
4. Curhan GC, Willett WC, Knight EL, Stampfer MJ. Dietary factors and the risk of incident kidney
stones in younger women: Nurses' Health Study II. Arch Intern Med. 2004 Apr 26 [cited 2013 Jul
2];164(8):885-91. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15111375
5. Taylor EN, Curhan GC. Dietary calcium from dairy and non-dairy sources and risk of
symptomatic kidney stones. J Urol. 2013 Mar 24 [cited 2013 Jul 5]. doi: S0022-5347(13)03862-7.
[Epub ahead of print]. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/23535174
6. Wallace RB, Wactawski-Wende J, O'Sullivan MJ, Larson JC, Cochrane B, Gass M, et al. Urinary
tract stone occurrence in the Women's Health Initiative (WHI) randomized clinical trial of calcium
and vitamin D supplements. Am J Clin Nutr. 2011 Jul [cited 2013 Jul 2];94(1):270-7. Abstract
available from: https://www.ncbi.nlm.nih.gov/pubmed/21525191
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 57. Food and Nutrition Board, Institute of Medicine, Dietary Reference Intakes for calcium and
vitamin D. Washington, D.C.: The National Academies Press; 2010 [cited 2013 Jul 2]. Available
from: http://www.ncbi.nlm.nih.gov/books/NBK56070/
8. Heilberg IP, Goldfarb DS. Optimum nutrition for kidney stone disease. Adv Chronic Kidney Dis.
2013 Mar [cited 2013 Jul 2];20(2):165-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/23439376
Q2: What dietary and lifestyle factors have been associated with an increased risk of developing
renal calculi (kidney stones) in individuals with no previous history of kidney stones?
Subcategory: Intervention
Updated: 2014-07-03
Key Practice Point #1
A high intake of animal protein (>2 g/kg body weight per day) alters urinary uric acid, calcium and citrate
excretion rate, which are correlated with kidney stone formation. Observational data on the effects of
animal protein intake on the risk for kidney stones are conflicting, with an association between high animal
protein intake (>75 g/day) and increased risk of kidney stones observed primarily in healthy normal weight
men (BMI 2
g/kg body weight/day prepared by supplementing the basal diet with red meat) increased urinary
calcium excretion (1) and may result in hypocitraturia, a risk factor for kidney stones (2). The
effect of protein was thought to occur due to the release of calcium from bone following excess
H+ buffering.
b. Observational data from a cohort of 45,619 men aged 40 to 75 years with no history of kidney
stones (Health Professionals Follow-up Study) showed that a high intake of animal protein was
associated with an increased risk of stone formation (RR for men with protein intake in the
highest quintile (>75 g/day) as compared to those in the lowest quintile,1.33; 95% CI, 1.00 to
1.77) (3). However, follow-up data showed that animal protein intake was only associated with an
increased risk of forming kidney stones in men with a BMI 25 kg/m2.
c. In a cohort of 91,732 women aged 34 to 59 years with no history of kidney stones (Nurses'
Health Study I), no association was observed between the intake of animal protein and risk of
kidney stones (5). This was confirmed in the Nurses' Health Study II in women aged 27 to 44
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 6years with no history of kidney stones (RR for highest intake of animal protein compared to
lowest intake = 0.84, 95% CI, 0.68 to 1.04) (6).
References
1. Kok DJ, Iestra JA, Doorenbos CJ, Papapoulos SE. The effects of dietary excesses in animal
protein and in sodium on the composition and the crystallization kinetics of calcium oxalate
monohydrate in urines of healthy men. J Clin Endocrinol Metab. 1990 Oct [cited 2013 Jul 2];71
(4):861-7. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/2401715
2. Heilberg IP, Goldfarb DS. Optimum nutrition for kidney stone disease. Adv Chronic Kidney Dis.
2013 Mar [cited 2013 Jul 2];20(2):165-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/23439376
3. Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study of dietary calcium and
other nutrients and the risk of symptomatic kidney stones. N Engl J Med. 1993 Mar 25 [cited
2013 Jul 2];328(12):833-8. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/9092314
4. Taylor E, Stampfer M, Curhan G. Dietary factors and the risk of incident kidney stones in men:
new insights after 14 years of follow up. J Am Soc Nephrology. 2004 Dec [cited 2013 Jul
2];15:3225-32. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15579526
5. Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary
calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney
stones in women. Ann Intern Med. 1997 Apr 1 [cited 2013 Jul 2];126(7):497-504. Abstract
available from: https://www.ncbi.nlm.nih.gov/pubmed/9092314
6. Curhan GC, Willett WC, Knight EL, Stampfer MJ. Dietary factors and the risk of incident kidney
stones in younger women: Nurses' Health Study II. Arch Intern Med. 2004 Apr 26 [cited 2013 Jul
2];164(8):885-91. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15111375
Key Practice Point #2
Evidence from observational studies suggests that fructose intake (free fructose and total fructose) is
associated with an increased risk of kidney stones in healthy adults. Studies examining beverage intake
in particular identify that the consumption of soda beverages and sweetened drinks such as punch are
associated with an increased risk of kidney stones in healthy adults. It is recommended that individuals
follow Healthy Eating Guidelines, which limit the consumption of sweetened beverages and foods with
added sugar.
Grade of Evidence: C
Evidence
a. An evaluation of fructose intake (free fructose and total fructose) from three large cohorts
(n=241,538) with no previous history of kidney stones (the Health Professionals Follow-up Study
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 7and the Nurses' Health Study I and II) identified an increased risk of kidney stones in all groups
(1). The main sources of free fructose were sugar-sweetened soft drinks, fruit juice and fruit. The
main sources of total fructose (calculated as free fructose plus half of sucrose) included table
sugar, sugar-sweetened soft drinks, fruit juices, fruit punch and sweetened desserts. For total
fructose intake, when comparing the highest (~12% of energy) to the lowest (~7% of total
energy) quintiles, the multivariate adjusted relative risk of kidney stones was 1.27, 1.37, and 1.35
in the HPFS, NHS I and NHS II, respectively.
b. Analysis of data obtained from the HPFS and NHS I and II (n=194,095) over a median follow up of
eight years examined the association between type of beverage consumed and the risk of kidney
stones (2). Comparing the highest (i.e. ≥1 serving /day) to lowest consumption (i.e.a. An evaluation of fatty acid intake (including fish oil supplements) and incidence of kidney stones
in three large cohorts (n=194,095) with no previous history of kidney stones (the Health
Professionals Follow-up Study and the Nurses' Health Study I and II), did not observe an
association between intake of arachidonic acid or linoleic acid and risk of kidney stones (1). In
the Nurses' Health Study I cohort, older women (45-70 years) in the highest quintile of EPA and
DHA intake had a higher risk of stone formation compared to women in the lowest quintile
(relative risk, 1.28; 95% CI, 1.04 to 1.56); however, this association was not observed in the other
two cohorts.
Rationale
Elevated levels of arachidonic acid, which have been observed in cell membranes of calcium stone-
formers, may promote hypercalciuria and hyperoxaluria (1). The intake of omega-3 fatty acids, such as
eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may decrease the arachidonic acid
content of cell membranes and reduce urinary excretion of calcium and oxalate. Thus, it has been
suggested that a higher intake of EPA and DHA (either dietary sources or fish oil supplementation) may
reduce the risk of kidney stones (2); however, no clinical trials have evaluated the effect of omega-3 fatty
acids on development of kidney stones (3).
References
1. Taylor EN, Stampfer MJ, Curhan GC. Fatty acid intake and incident nephrolithiasis. Am J Kidney
Dis. 2005 Feb [cited 2013 Jul 2];45(2):267-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/15685503
2. Donadio JV. n-3 fatty acids and their role in nephrologic practice. Curr Opin Nephrol Hypertens.
2001 Sep [cited 2013 Jul 2];10(5):639-42. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/11496058
3. Fassett RG, Gobe GC, Peake JM, Coombes JS. Omega-3 polyunsaturated fatty acids in the
treatment of kidney disease. Am J Kidney Dis. 2010 Oct [cited 2013 Jul 2];56(4):728-42.
Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/20493605
Key Practice Point #4
Increasing salt intake (sodium chloride, but not other sources of sodium) increases excretion of urinary
calcium, a risk factor for kidney stones. Results from one cohort study suggest that a high intake of
dietary salt (i.e. >4000 mg/day sodium] increases the risk for kidney stones in adults with no history of
kidney stones. This observation requires confirmation from other studies before a recommendation for
sodium can be made to reduce risk of kidney stones.
Grade of Evidence: C
Evidence
a. Clinical studies in healthy subjects indicate that salt consumption is associated with increased
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 9urinary calcium excretion (urinary calcium excretion increases approximately 0.5 to 1.0 mmol
(25 to 40 mg) for each 100 mmol (2300 mg) increase in dietary sodium in normal adults) (1).
b. An association between salt intake and the risk of kidney stones was reported in the Nurses'
Health Study I (RR among women in the highest quintile of sodium intake [>4081 mg/day]
compared with those in the lowest quintile of sodium intake [5. Borghi L, Meschi T, Maggiore U, Prati B. Dietary therapy in idiopathic nephrolithiasis. Nutr Rev.
2006 Jul [cited 2013 Jul 2];64(7 Pt 1):301-12. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/16910218
6. Taylor EN, Curhan GC. Demographic, dietary, and urinary factors and 24-h urinary calcium
excretion. Clin J Am Soc Nephrol. 2009 Dec [cited 2013 Jul 2];4(12):1980-7. Abstract available
from: https://www.ncbi.nlm.nih.gov/pubmed/19820135
Key Practice Point #5
Data from clinical trials in healthy adults suggests a low to moderate increased risk of kidney stones
associated with calcium supplements, including calcium supplements combined with vitamin D. The data
is dominated by a large clinical trial (Women's Health Initiative) in which healthy postmenopausal women
who took calcium (1000 mg/day) and vitamin D (400 IU/day) supplements over a seven-year period showed
an increased incidence of kidney stones compared to those taking placebo.
It is recommended that individuals achieve the Dietary Reference Values. Natural calcium-rich foods are
the preferred source of calcium; if calcium supplementation is necessary to meet needs, low dose
supplementation should be considered so that the intake of calcium from both diet and supplements does
not exceed 2000 mg/day.
Grade of Evidence: B
Evidence
a. Fourteen-year follow-up data from the U.S. Male Health Professionals Follow-up Study, did not
identify an association between vitamin D intake and the risk for kidney stones (1).
b. In women aged 34 to 59 years with no history of kidney stones from the Nurses' Health Study I,
women who took a calcium supplement had a higher risk for stone formation compared to those
who did not (RR=1.20; 95% CI, 1.02 to 1.41); although dietary calcium intake was inversely
associated with the risk for kidney stones (2). The authors report that of the two-thirds of women
who took a calcium supplement, the calcium supplement was not consumed with a meal or was
consumed with meals in which oxalate content was low, suggesting that the different effects
caused by the type of calcium consumed may be due to the timing of calcium ingestion relative
to the amount of oxalate consumed.
c. In an examination of younger women aged 27 to 44 years with no history of kidney stones from
the Nurses' Health Study II, supplemental calcium intake was not associated with risk of stone
formation (3).
d. The Women's Health Initiative (WHI) study examined the effect of calcium (1000 mg/day) and
vitamin D (400 IU/day) supplements for preventing hip fractures in 36,282 postmenopausal
women over a seven-year period (4). An adverse effect of this intervention was an increased
incidence of kidney stones (in women with no previous history of renal calculi) in the
supplemented compared to the placebo group (hazard ratio, 1.17; 95% CI,1.02-1.34). No
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 11differences in incidence of stones were observed when other factors were considered, including
demographic (e.g. age, ethnicity, education, smoking status), medical history, BMI, dietary
intake (e.g. total energy, protein, fat, alcohol, caffeine, vitamin C, calcium, sodium, iron,
potassium, oxalic acid) or use of calcium supplements at baseline (5).
e. A 2009 Cochrane review examining the effect of vitamin D alone or with calcium on preventing
fractures identified 11 trials (46,537 participants) that report adverse effects of supplements on
kidney stones or renal insufficiency (6). In these studies vitamin D with or without calcium
contributed to a small but significant increase in the incidence of kidney stones or renal
insufficiency (RR=1.16; 95% CI, 1.02 to 1.33). The authors indicate that the adverse effects were
dominated by the WHI study cited above (4) in which calcium supplements were also given with
vitamin D; however, significant differences in the incidence of renal calculi were observed between
the subgroups when vitamin D was given with and without calcium supplements.
f. A 2011 Cochrane review examining the effect of vitamin D on mortality included 50 RCTs of which
four trials (42,876 participants) reported an increased risk of nephrolithiasis using vitamin D3
combined with calcium (RR=1.17; 95% CI, 1.02 to 1.34) (7).
g. The Institute of Medicine (IOM) set the tolerable upper intake for calcium of 2000 mg/day in
adults over 50 years (8). This level was established in response to the increased risk of kidney
stones that can occur when intake of calcium from both diet and supplements is greater than
2000 mg/day (8). This consideration is based largely on the WHI trial (4). To support strong,
healthy bones, the IOM recommends that calcium intakes from food and supplements for women
over 50 should be 1200 mg daily, 1000 mg/day for men aged 51-70 years and 1200 mg/day for
men older than 70 years of age, not exceeding the tolerable upper intake of 2000 mg/day
calcium for adults over the age of 51 years (8).
Rationale
The difference in findings between dietary and supplemental calcium have been attributed to different
timing of ingestion, whereby ingesting supplements without food leads to increased calcium absorption
and urinary excretion with no effect on absorption and excretion of oxalate (9).
In addition, some individuals with hypercalciuria have increases in the circulating concentration and
production rate of 1,25-dihyroxyvitamin D, leading to hyperabsorption of intestinal calcium (10), and
increasing risk for stone formation (11).
References
1. Taylor E, Stampfer M, Curhan G. Dietary factors and the risk of incident kidney stones in men:
new insights after 14 years of follow up. J Am Soc Nephrology. 2004 Dec [cited 2013 Jul 2];15
(12):3225-32. Abstract available from:https://www.ncbi.nlm.nih.gov/pubmed/15579526
2. Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ. Comparison of dietary
calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney
stones in women. Ann Intern Med. 1997 Apr 1 [cited 2013 Jul 2];126(7):497-504. Abstract
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 12available from: https://www.ncbi.nlm.nih.gov/pubmed/9092314
3. Curhan GC, Willett WC, Knight EL, Stampfer MJ. Dietary factors and the risk of incident kidney
stones in younger women: Nurses' Health Study II. Arch Intern Med. 2004 Apr 26 [cited 2013 Jul
2];164(8):885-91. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15111375
4. Jackson RD, LaCroix AZ, Gass M, Wallace RB, Robbins J, Lewis CE, et al; Women's Health
Initiative Investigators. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J
Med. 2006 Feb 16 [cited 2013 Jul 2];354(7):669-83. Abstract available
from: https://www.ncbi.nlm.nih.gov/pubmed/16481635
5. Wallace RB, Wactawski-Wende J, O'Sullivan MJ, Larson JC, Cochrane B, Gass M, et al.
Urinary tract stone occurrence in the Women's Health Initiative (WHI) randomized clinical trial of
calcium and vitamin D supplements. Am J Clin Nutr. 2011 Jul [cited 2013 Jul 2];94(1):270-7.
Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/21525191
6. Avenell A, Gillespie W, Gillespie L, O'Connell D. Vitamin D and vitamin D analogues for
preventing fractures associated with involutional and post-menopausal osteoporosis. Cochrane
Database Syst Rev. 2009 Apr 15 [cited 2013 Jul 2];(2):CD000227. Abstract available from:
from: https://www.ncbi.nlm.nih.gov/pubmed/19370554
7. Bjelakovic G, Gluud LL, Nikolova D, Whitfield K, Wetterslev J, Simonetti RG, et al. Vitamin D
supplementation for prevention of mortality in adults. Cochrane Database Syst Rev. 2011 Jul 6
[cited 2013 Jul 2];(7):CD007470. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/21735411
8. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for calcium and
vitamin D. Washington, D.C.: The National Academies Press; 2010 [cited 2013 Jul 6]. Available
from: http://www.ncbi.nlm.nih.gov/books/NBK56070/
9. Heilberg IP, Goldfarb DS. Optimum nutrition for kidney stone disease. Adv Chronic Kidney Dis.
2013 Mar [cited 2013 Jul 2];20(2):165-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/23439376
10. Broadus AE, Insogna KL, Lang R, Ellison AF, Dreyer BE. Evidence for disordered control of 1,25-
dihydroxyvitamin D production in absorptive hypercalciuria. N Engl J Med. 1984 Jul 12 [cited
20014 May 14];311(2):73-80. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/6330548
11. Borghi L, Meschi T, Maggiore U, Prati B.Dietary therapy in idiopathic nephrolithiasis. Nutr Rev.
2006 Jul [cited 2014 May 14];64(7 Pt 1):301-12. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/16910218
Key Practice Point #6
Increased dietary oxalate and decreased dietary calcium intake result in increased urinary oxalate
excretion. Observational data suggests a modest increased risk of kidney stones at high oxalate intake
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 13(median 280 mg/day for women and 328 mg/day for men) with a greater risk in men who consumed a
lower intake of dietary calcium. No trials have examined the effect of lowering dietary oxalate on stone
formation. Current data are insufficient to implicate dietary oxalate as a major risk factor for kidney stones
in healthy adults, therefore a dietary oxalate restriction should not be routinely recommended to prevent
kidney stones in otherwise healthy adults.
Grade of Evidence: C
Evidence
a. A narrative review examining dietary components thought to be involved in the pathophysiology of
kidney stones identifies that it is well established that urinary oxalate increases with increased
dietary oxalate (1). This is based on metabolic studies in healthy adults, which have reported
urinary oxalate excretion ranging from 24-42% on a diet ranging from 10 to 250 mg/day
oxalate (2). The review authors emphasize that oxalate absorption is highly dependent on
calcium intake, with increasing absorption and excretion occurring with decreasing dietary
calcium, and suggest that increasing calcium intake (especially if intake is low), may be more
effective at decreasing oxalate excretion than decreasing dietary oxalate (1). No trials were
identified that examined the effect of lowering dietary oxalate on stone formation. Observational
studies have not reported differences in dietary oxalate intake in stone formers compared to non-
stone formers, but have reported a small increase in risk with increased oxalate intake (as
described below):
An examination of oxalate intake and incidence of kidney stones in three large cohorts
with no previous history of kidney stones (the Health Professionals Follow-up Study and
the Nurses' Health Study I and II) indicates a mean oxalate intake of 214 mg/day in
men, 185 mg/day in older women and 183 mg/day in younger women which were not
different between stone formers and non-stone formers (3). More than 40% of oxalate
intake came from spinach. The relative risk (RR) for kidney stones for participants in the
highest compared to the lowest quintile of dietary oxalate intake was 1.22 (95% CI, 1.03
to 1.45) for men (median oxalate intake at highest quintile versus lowest quintile for men
= 328 mg/day and 106 mg/day) and 1.21 (95% CI, 1.01 to 1.44) for older women
(median oxalate intake at highest quintile versus lowest quintile for older women = 287
mg/day and 87 mg/day). No increased risk was found in younger women. Risk was
higher in men with lower dietary calcium intake (in men with dietary calcium below the
median (755 mg/d), RR of the highest compared with lowest quintile of dietary oxalate =
1.46 (95% CI 1.11 to 1.93). The authors report that the increased risk was small and the
results do not implicate dietary oxalate as a major risk factor for kidney stones.
Rationale
Most (~80%) kidney stones contain calcium and the majority of calcium stones consist primarily of
calcium oxalate (3). Higher levels of urinary oxalate increases the risk for calcium oxalate kidney stones.
Urinary oxalate is derived from both dietary sources and endogenous metabolism; consequently dietary
intake alone cannot predict oxalate excretion (1). Furthermore, absorption of dietary oxalate is variable,
but tends to be higher in individuals with low calcium intake, those with fat malabsorption, and in
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 14individuals with a history of kidney stones. It is therefore likely that a dietary oxalate restriction would be
more efficacious in individuals with increased absorption and hyperoxaluria (1).
References
1. Heilberg IP, Goldfarb DS. Optimum nutrition for kidney stone disease. Adv Chronic Kidney Dis.
2013 Mar [cited 2013 Jul 2];20(2):165-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/23439376
2. Holmes RP, Goodman HO, Assimos DG. Contribution of dietary oxalate to urinary oxalate
excretion. Kidney Int. 2001 Jan [cited 2013 Jul 3];59(1):270-6. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/11135080
3. Taylor EN, Curhan GC. Oxalate intake and the risk for nephrolithiasis. J Am Soc Nephrol. 2007
Jul [cited 2013 Jul 2];18(7):2198-204. Available from:
https://www.ncbi.nlm.nih.gov/pubmed/17538185
Key Practice Point #7
Observational studies that have controlled for age and dietary intake, suggest that weight gain and obesity
increase the risk of kidney stones in healthy adults; the magnitude of risk is greater in women than in
men.
Diabetes and a diagnosis of metabolic syndrome also appear to increase the risk of kidney stone
formation.
Strategies to prevent weight gain, obesity and development of diabetes/metabolic syndrome may be
beneficial to prevent kidney stones in otherwise healthy adults.
Grade of Evidence: C
Evidence
a. A prospective study of three large cohorts (Nurses Health Study I and II and Health Professionals
Follow-up Study) found that obesity and weight gain increased the risk of kidney stone formation
and the magnitude of risk appears to be greater in women than in men (1). After adjusting for
age, dietary factors, fluid intake, and thiazide use, the relative risk (RR) for stone formation in
men with a BMI ≥30 versus a BMI of 21-23 was 1.33. For women in the same BMI categories,
the RR for older women was 1.90 and for younger women the RR was 2.09. For men who gained
more than 16 kg since 21 years of age versus those who did not gain weight, the RR was 1.39.
For women who gained the same amount of weight the RR was 1.70 for older and 1.82 for
younger women. Waist circumference was also associated with risk for both men and women.
b. An evaluation by the same authors of the relationship between diabetes and nephrolithiasis in
three large cohorts reports that diabetes is a risk factor for the development of kidney stones (RR
for stone disease in individuals with diabetes compared to those without = 1.38 in older women,
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 151.67 in younger women and 1.31 in men) (2). The authors comment that studies are required to
determine whether the increased risk of diabetes is due to insulin resistance.
c. A systematic review of studies (published to 2013) examining the relationship between metabolic
syndrome and nephrolithiasis identified five cross sectional studies (n=209,120; mean age = 44.9
years) (3). A pooled meta-analysis identified a higher prevalence of nephrolithiasis associated
with a diagnosis of metabolic syndrome. Significant between-study heterogeneity and evidence of
publication bias was reported; when two missing studies were included, the adjusted odds ratio
was 1.21 (95% CI, 1.03 to 1.41).
Rationale
Higher BMI is associated with lower urine pH which is the suggested mechanism for the higher prevalence
of uric acid stones in obese adults (4). A higher BMI is also associated with a higher urine oxalate
excretion, which may increase the risk of calcium oxalate stones.
Reduced insulin sensitivity and hyperinsulinemia, (characteristics of diabetes and metabolic syndrome)
have renal effects contributing to stone formation in the urine (3).
References
1. Taylor EN, Stampfer MJ, Curhan GC. Obesity, weight gain, and the risk of kidney stones. JAMA.
2005 Jan [cited 2013 Jul 3];293(4):455-62. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/15671430
2. Taylor EN, Stampfer MJ, Curhan GC. Diabetes mellitus and the risk of nephrolithiasis. Kidney
Int. 2005 Sep [cited 2013 Jul 3];68(3):1230-5. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/16105055
3. Rendina D, De Filippo G, D'Elia L, Strazzullo P. Metabolic syndrome and nephrolithiasis: a
systematic review and meta-analysis of the scientific evidence. J Nephrol. 2014 Apr 3. [Epub
ahead of print] [cited 2014 May 14]. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/24696310
4. Heilberg IP, Goldfarb DS. Optimum nutrition for kidney stone disease. Adv Chronic Kidney Dis.
2013 Mar [cited 2013 Jul 2];20(2):165-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/23439376
Q3: For the prevention of renal calculi (kidney stones), is a vegetarian diet (especially one high
in dietary fibre, potassium and magnesium) associated with a lower risk of developing kidney
stones compared to a mixed diet containing animal protein?
Subcategory: Intervention
Updated: 2014-07-03
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 16Key Practice Point #1
Different types of diets may have an effect on kidney stone prevention through effects on altering urinary
uric acid and citrate excretion, urine volume and urinary pH. Diets low in animal protein and high in
vegetables and fruit provide fibre and potassium and deliver an alkali load to the kidneys, which may lower
the risk of calcium stone formation for individuals with and without a history of kidney stones.
However, there is a lack of clinical trials comparing the effects of a vegetarian and non-vegetarian diet on
preventing kidney stones. Limited data from one clinical trial suggests that diet low in animal protein and
high in fruit, vegetables and whole grains increases the risk of recurrent stones compared to a control diet.
Additional high quality trials are required to confirm this observation before any conclusions can be made
regarding a vegetarian diet.
Grade of Evidence: C
Evidence
a. In an open-label clinical trial conducted in 10 healthy men, the risk of uric acid crystallization was
was highest on the ingestion of a self-selected meat-containing Western-type diet, due to high
urinary uric acid excretion and acidic urinary pH (1). The intake of a balanced ovo-lacto
vegetarian diet with a moderate amount of animal protein and a high alkali-load with fruits and
vegetables (28 grams of animal protein and 6500 mg of potassium per day) resulted in the lowest
risk of uric acid crystallization (reduction in the risk of uric acid crystallization of 93%) compared
to the omnivorous diets (56 grams of animal protein and 3600 mg of potassium per day).
b. An open-label clinical trial conducted in 10 healthy adults demonstrated that the consumption of
a low carbohydrate (~25 g/day) high protein (~165 g/day) diet for six weeks delivers a significant
acid load to the kidney that increases the risk for stone formation (2).
c. A narrative review of dietary factors implicated in the development of kidney stones, indicates
that a substitution of animal protein intake with a high intake of fruits and vegetables is
associated with increased urine pH and volume (due to high water content of fruits and
vegetables) (3). As a result, urinary citrate is increased, potassium excretion increases and
ammonium excretion is reduced. This is supported by observational studies, which have shown
an association between higher potassium intake and decreased incidence of kidney stones in
men and older women (but not younger women). The authors suggest that urinary alkalinization
provided by a more vegetarian diet is beneficial for preventing stone formation, particularly uric
acid stones.
d. Published after the aforementioned review (3), a cross-sectional study of 2,561 individuals from
the Health Professionals Follow-up study and Nurses’ Health Studies I and II examined dietary
factors associated with urinary citrate excretion (4). Based on two, 24-hour urine collections and
dietary intake from food frequency questionnaires, nondairy animal protein intake was associated
with lower urinary citrate excretion (increased risk of kidney stones). In contrast, potassium
intake was associated with increased urinary citrate excretion (decreased risk of kidney stones)
in both individuals with and without a history of nephrolithiasis.
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 17e. An Agency for Healthcare Research and Quality (AHRQ) review examining the efficacy and harm
of dietary interventions for preventing recurrent kidney stones did not identify any studies directly
comparing a vegetarian to a non-vegetarian diet (5). One trial of a multicomponent diet was
identified, in which 99 participants with one previous incidence of calcium oxalate stones, were
randomized to a low animal protein (56-64 g/day); high fruit, vegetable and whole grains;
increased bran (1/4 cup/day) and low purine (75 mg/day) diet or a control diet for four years (6).
Both groups were advised to consume two dairy servings and six to eight glasses of liquid/day.
Results showed a higher rate of stone recurrence in the multicomponent intervention than the
control group (7.1 versus 1.2 per 100 person years). The study authors conclude that a low
animal protein, high fibre, high fluid diet provides no advantage over increasing fluid intake alone
(6). The AHRQ report concludes that there is limited evidence that a low animal protein; high
fruit, vegetables and whole grains; high fibre and low purine diet increases the risk of recurrent
stones compared to a control diet (5).
Comments
A vegetarian diet may increase intake of dietary oxalates and vitamin C, factors that may have a negative
effect on stone formation (4). On the other hand, vegetables and fruits demonstrate anti-lithogenic effects
because they are associated with increased urinary volume, potassium, citrate, magnesium and pH (7).
Rationale
A vegetarian diet may increase intake of dietary oxalates and vitamin C, factors that may promote stone
formation (7). On the other hand, vegetables and fruits demonstrate anti-lithogenic effects because they
are associated with increased urinary volume, potassium, citrate, magnesium and pH (8). The proposed
mechanisms of action by which dietary factors inhibit the formation of calcium stones include (8):
Fibre: Foods high in fibre contain large quantities of phytate, which may inhibit the formation of
calcium stones. A benefit has been demonstrated with the consumption of 10-15 grams of bran
per day.
Potassium: Dietary potassium restriction can increase urinary calcium excretion by reducing the
alkali load, which increases risk of stone formation.
Magnesium: Magnesium complexes with oxalate, potentially reducing oxalate absorption in the
gastrointestinal tract and decreasing calcium oxalate supersaturation in the urine.
References
1. Siener R, Hesse A. The effect of a vegetarian and different omnivorous diets on urinary risk factors
factors for uric acid stone formation. Eur J Nutr. 2003 Dec [cited 2013 Jul 2];42(6):332-337.
Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/14673606
2. Reddy ST, Wang CY, Sakhaee K, Brinkley L, Pak CY. Effect of low-carbohydrate high-protein
diets on acid-base balance, stone-forming propensity, and calcium metabolism. Am J Kidney
Dis. 2002 Aug [cited 2013 Jul 2];40(2):265-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/12148098
3. Heilberg IP, Goldfarb DS. Optimum nutrition for kidney stone disease. Adv Chronic Kidney Dis.
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 182013 Mar [cited 2013 Jul 2];20(2):165-74. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/23439376
4. Mandel EI, Taylor EN, Curhan GC. Dietary and lifestyle factors and medical conditions
associated with urinary citrate excretion. Clin J Am Soc Nephrol. 2013 Jun; [cited 2014 May 14]8
(6):901-8. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/23449767
5. Fink HA, Wilt TJ, Eidman KE, Garimella PS, MacDonald R, Rutks IR, et al. Recurrent
nephrolithiasis in adults: comparative effectiveness of preventive medical strategies. Rockville
(MD): Agency for Healthcare Research and Quality (US); 2012 Jul. [cited 2013 Jun 19]. Report
No.: 12-EHC049-EF. Available from: https://www.ncbi.nlm.nih.gov/pubmed/22896859
6. Hiatt RA, Ettinger B, Caan B, Quesenberry CP Jr, Duncan D, Citron JT. Randomized controlled
trial of a low animal protein, high fiber diet in the prevention of recurrent calcium oxalate kidney
stones. Am J Epidemiol. 1996 Jul 1 [cited 2013 Jul 2];144(1):25–33. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/8659482
7. Grases F, Costa-Bauza A, Prieto RM. Renal lithiasis and nutrition. Nutr J. 2006 Sep [cited 2013
Jul 2];5:23. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/16956397
8. Meschi T, Maggiore U, Fiaccadori E, Schianchi T, Bosi S, Adorni G, et al. The effect of fruits and
vegetables on urinary stone risk factors. Kidney Int. 2004 Dec [cited 2013 Jul 2];66(6):2402-10.
Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15569332
Q4: What role does alcohol play in the prevention of kidney stones in individuals with no history
of kidney stones and for individuals with a history of developing kidney stones?
Subcategory: Intervention
Updated: 2014-07-17
Key Practice Point #1
Observational studies have suggested that moderate alcohol consumption (beer and wine, but not liquor)
may have a protective effect on kidney stone formation in healthy individuals. Individuals wishing to
consume alcohol should follow their country's Alcohol Guidelines.
For individuals with a history of kidney stones, alcohol may increase urinary uric acid excretion and
urinary calcium excretion, risk factors for developing calcium oxalate stones. An uncontrolled short-term
study in individuals with a history of calcium oxalate stones observed that a diet consisting of no alcohol,
moderate protein and high fluid, resulted in improvements in urinary risk factors for developing kidney
stones. This observation suggests that alcohol may have detrimental effects in individuals with a history of
kidney stones.
Grade of Evidence: C
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 19Evidence
a. Analysis of data obtained from the Health Professionals Follow-up Study and Nurses' Health
Study I and II (n=194,095) over a median follow up of eight years examined the association
between beverage consumption and the risk of kidney stones (1). Comparing the highest (i.e.
≥1 /day) to lowest consumption (i.e.1. Ferraro PM, Taylor EN, Gambaro G, Curhan GC. Soda and other beverages and the risk of kidney
kidney stones. Clin J Am Soc Nephrol. 2013 May 15. [Epub ahead of print] [cited 2013 Jul 5].
Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/23676355
2. Curhan GC, Willett WC, Speizer FE, Stampfer MJ. Beverage use and risk for kidney stones in
women. Ann Intern Med. 1998 Apr 1 [cited 2013 Jul 8];128(7):534-40. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/9518397
3. Curhan GC, Willett WC, Rimm EB, Spiegelman D, Stampfer MJ. Prospective study of beverage
use and the risk of kidney stones. Am J Epidemiol. 1996 Feb 1 [cited 2013 Jul 8];143(3):240-7.
Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/8561157
4. Siener R, Schade N, Nicolay C, von Unruh GE, Hesse A. The efficacy of dietary intervention on
urinary risk factors for stone formation in recurrent calcium oxalate stone patients. J Urol. 2005
May [cited 2013 Jul 8];173(5):1601-5. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/15821507
5. Morton AR, Iliescu EA, Wilson JW. Nephrology: 1. Investigation and treatment of recurrent
kidney stones. CMAJ. 2002 Jan 22 [cited 2013 Jul 8];166(2):213-18. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/11829004
6. Schlesinger N. Dietary factors and hyperuricaemia. Curr Pharm Des. 2005 [cited 2013 Jul 8];11
(32):4133-8. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/16375734
Q5: What role does caffeine play in the prevention of kidney stones in individuals with no history
of kidney stones and for individuals with a history of developing kidney stones?
Subcategory: Intervention
Updated: 2014-07-03
Key Practice Point #1
Epidemiological studies suggest that a moderate intake (i.e. ≥1 cup/day) of coffee, decaffeinated coffee
and tea may be protective against kidney stone formation in individuals with no history of kidney stones.
Those individuals wishing to consume caffeinated beverages should do so within current recommendations
[See Comments].
Although the effect of caffeine has not been studied in individuals with a history of kidney stones, these
individuals should limit caffeine intake (below current recommendations) because caffeine can increase
urinary calcium excretion and may modestly increase the risk of calcium oxalate stones.
Grade of Evidence: C
Evidence
a. Analysis of data obtained from the Health Professionals Follow-up Study and Nurses' Health
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 21Study I and II (n=194,095) over a median follow-up of eight years examined the association
between beverage consumption and the risk of kidney stones in individuals with no previous
history of nephrolithiasis (1). Comparing the highest (i.e. ≥1 cup/day) to lowest consumption (i.e.Key Practice Point #1
Observational data in men with no history of kidney stones supports an association between a high intake
of vitamin C and the risk of kidney stones. When considering dietary patterns; however, observational data
conducted in healthy men and women suggests that a DASH-style diet, which is high in vitamin C as well
as calcium, potassium, magnesium and oxalate, is associated with a reduced risk of developing kidney
stones. A restriction in dietary vitamin C intake is therefore not warranted to protect against the
development of kidney stones.
Grade of Evidence: C
Evidence
a. A 14-year cohort study of 45,619 healthy men over the age of 40 with no history of kidney stones
(Health Professionals Follow-up Study, HPFS) found an association between dietary vitamin C
intake and the risk of incident stone formation (1). After multivariate adjustment, men in the
highest quintile of dietary vitamin C intake (218 mg/day) compared to the lowest quintile (105
mg/day), showed an increased risk of kidney stones (RR 1.31; 95% CI, 1.08 to 1.60). Since
vitamin C-rich foods contain potassium and other compounds that may be protective against the
development of kidney stones, the authors suggest that individuals at risk for kidney stones,
should not limit the intake of dietary sources of vitamin C.
b. Analysis of data from the HPFS, in addition to the Nurses' Health Study (NHS) I (n=94,108 older
women with 18 years of follow up) and NHS II (101,837 younger women with 14 years of follow
up) examined the relation between a DASH-style diet and risk of kidney stones (2). For the
study, a DASH score was developed based on eight dietary components: high intake of
vegetables and fruit, nuts and legumes, low fat dairy products, and whole grains; and a low
intake of red and processed meats, sodium, and sweetened beverages. Results showed that
participants with a higher DASH score had a higher intake of vitamin C in addition to higher
intakes of calcium, potassium, magnesium and oxalate, and lower intakes of sodium. Comparing
the highest to lowest DASH score (average vitamin C intake ~450 mg/day versus 250 mg/day),
the multivariate risk for kidney stones was 0.55 for men, 0.58 for older women and 0.60 for
younger women.
c. An RCT examined the effects of a DASH dietary pattern on urinary risk profile in recurrent stone
formers with hyperoxaluria (3). Of the 57 participants randomized to either a DASH diet or a low
oxalate diet for eight weeks, 41 (72%) completed the trial. Results showed a trend for increased
urinary oxalate excretion and decreased oxalate supersaturation on the DASH diet, but this was
not significant, which the authors attributed to the small sample size.
Comments
The effect of a single dietary factor can be masked or overwhelmed by other factors in a particular food.
For instance, some foods that contain vitamin C and oxalate, both of which may increase urinary oxalate,
also contain citrate and potassium, which are stone inhibitors (4).
References
Nephrology - Kidney Stones
© 2019 Dietitians of Canada. All rights reserved. PAGE 231. Taylor E, Stampfer M, Curhan G. Dietary factors and the risk of incident kidney stones in men:
new insights after 14 years of follow up. J Am Soc Nephrology. 2004 Dec [cited 2013 Jul
2];15:3225-32. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15579526
2. Taylor EN, Fung TT, Curhan GC. DASH-style diet associates with reduced risk for kidney
stones. J Am Soc Nephrol. 2009 Oct [cited 2013 Jul 9];20(10):2253-9. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/19679672
3. Noori N, Honarkar E, Goldfarb DS, Kalantar-Zadeh K, Taheri M, Shakhssalim N, et al. Urinary
lithogenic risk profile in recurrent stone formers with hyperoxaluria: a randomized controlled trial
comparing DASH (Dietary Approaches to Stop Hypertension)-style and low-oxalate diets. Am J
Kidney Dis. 2014 Mar [cited 2014 May 16];63(3):456-63. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/24560157
4. Taylor EN, Curhan GC. Role of nutrition in the formation of calcium-containing kidney stones.
Nephron Physiol. 2004 [cited 2013 Jul 9];98(2):55-63. Abstract available from:
https://www.ncbi.nlm.nih.gov/pubmed/15499216
Key Practice Point #2
Vitamin C supplementation (>1000 mg/day) increases urinary oxalate, which is associated with an
increased risk for kidney stones. Observational studies in men with no history of kidney stones have
identified that vitamin C supplementation is associated with an increased risk of developing kidney stones.
[C]
For individuals with a history of kidney stones, high dose vitamin C supplements are not recommended
[C]. For the general population, the consumption of vitamin C supplements beyond the UL (2000 mg/day)
is not recommended [B]. Additional research is necessary to examine the association between vitamin C
supplementation and kidney stone occurrence.
Grade of Evidence: B & C
Evidence
a. Epidemiological studies of vitamin C and kidney stone risk from the U.S. have produced
conflicting evidence. In a study of 45,619 men with no history of kidney stones (Health
Professionals Follow-up Study), the multivariate relative risk of developing kidney stones was
1.41 (95% CI, 1.11 to 1.80) for individuals consuming supplements containing more than 1000
mg/day of ascorbic acid compared with those who consumed less then 90 mg/day (1). However,
an earlier report of 85,557 women in the Nurses' Health study found no association between
women consuming >1500 mg/day vitamin C compared with women in the lowest category of
vitamin C intake (two-fold increased risk of kidney stones after adjusting for multiple factors including age,
education, BMI, dietary intakes of calcium, magnesium, potassium, vitamin B6, vitamin C, tea
and coffee (multivariate RR, 1.92; 95% CI, 1.33 to 2.77). Multivitamin use was not associated
with an increased risk (RR, 0.86; 95% CI, 0.62 to 1.19). The dose of vitamin C supplements was
not collected from participants.
c. Oxalate is a risk factor for kidney stones and urinary oxalate is used as an indicator of oxalate
formation (1,4-6). A small amount of vitamin C is endogenously converted to oxalate and also
appears to increase the absorption of dietary oxalate (5,6).
An open-label study in which large doses of vitamin C (1000 or 2000 mg/day for three
days) were given to calcium-forming individuals and to healthy controls, showed that
vitamin C supplements (≥1000 mg/day) increased urinary excretion of oxalate and
increased the risk of calcium oxalate crystallization in groups (5).
In a double-blind, randomized, crossover study of 12 normal subjects and 12 calcium
oxalate stone formers over two six-day experimental periods, supplementation with 1000
mg vitamin C two times per day resulted in increases of urinary oxalate by 33% in stone
formers compared to 20% in non-stone formers (4).
The effect of vitamin C supplements (1000 mg twice/day for six days) on urinary oxalate
compared to no supplement were studied in a randomized crossover design in 29
individuals with a history of calcium oxalate stones (stone formers) and 19 healthy
controls in a metabolic setting where subjects also received a low-oxalate diet (6). In
40% of participants (both stone formers and controls), vitamin C increased urinary
oxalate and risk for oxalate kidney stones. The investigators conclude that because an
individual's response to vitamin C supplements is not predictable, intake of vitamin C
≥2000 mg/day should be considered cautiously, even for those individuals without a
history of stone formation (6).
Comments
See Dietary Reference Values for vitamin C.
The Tolerable Upper Intake Level (UL) for vitamin C (ascorbic acid) set by the Institute of Medicine is 2000
mg/day (7).
Rationale
A small percentage (1.5%) of ingested ascorbic acid is converted in vivo to oxalate (6), which is excreted
without further metabolism in the urine over 24 hours. If vitamin C supplements are taken, the increased
urinary oxalate may increase the risk of calcium oxalate kidney stones.
References
1. Taylor E, Stampfer M, Curhan G. Dietary factors and the risk of incident kidney stones in men:
new insights after 14 years of follow up. J Am Soc Nephrology. 2004 Dec [cited 2013 Jul
2];15:3225-32. Abstract available from: https://www.ncbi.nlm.nih.gov/pubmed/15579526
Nephrology - Kidney Stones
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